Now that I can consistently pull shots in the 25-30 sec. window, relying on skill rather than luck, I can now pay closer attention to another key variable: Sirena's temperature. Though I do not have the tools to take precise measurements, the principles of temp-surfing can still be applied to the Sirena as well as any other single-boiler macchina.

As we know, different beans require not only different grinds, but temperatures as well, to release their full potential. If you have noticed that "cosmetic" gauge on the dashboard, you may have wondered how it could possibly help, esp. as it has no numbers. Fortunately the gauge does reveal a predictable pattern of boiler cycling and provides reference points to help time your shots for your particular beans.

Obviously we cannot rely on Starbucks or Saeco for help in this matter; they will say, after the lights stop blinking, you can pull your shot anytime. Customer Service has no idea what the 12 o'clock mark means in degrees, if each increment represents 1 degree or 5 degrees, Celsius or Fahrenheit, or the maximum & minimum temperatures of the thermostat deadband. But even without this information, we know up from down, and the key is knowing when the boiler element starts and stops. These are my initial observations; I will refer to the 12 o'clock mark as "M" (for "midnight", or midday, if you prefer). Once the Sirena has warmed up, the needle drifts back & forth, always within +/- 4 degrees of M.

The boiler cycles on & off even with the lights always solid (non-blinking). From a cold start, the machine is supposedly ready to brew at M-2 in about 2 to 2.5 minutes. Of course that's not true, because the rest of the brewpath needs more time to warm up. After 1/2 hr. or so, the true cycling pattern emerges:

At M-3.5, the boiler is at the bottom of its deadband; at this point, a faint CLICK tells you when the boiler element turns on. The needle rises quickly until M-1.5; if the lights were blinking, as they do after pulling shots or steaming, they will be solid now. At this point a second, slightly louder CLICK tells you (I believe) that the boiler has shut off. The needle will continue rising until it peaks out at M+3 (or rarely, M+4) in about 1 minute. Then it drifts downward very slowly; one can speed up the temperature drop by bleeding hot water from the steam wand or pulling a blank shot. When it falls to M-3.5, the cycle repeats itself.

As you can see, there are at least two ways to temp-surf a macchina: you can pull your shot as the temperature is rising, or as it's falling (known generally as "forward" & "reverse" temp-surfing). Because the Sirena's boiler is small and heats up so rapidly, it is inherently harder to catch a desired temperature on the rise, unless you're aiming for the top end. In that case you probably want to pull your shot soon after the second click. Otherwise, unless you have kung-fu reflexes, I would advise reverse-surfing; it gives you more time and may give more consistent results. If, for ex., at the start of the cycle, new (cold) water from the reservoir is introduced into the boiler, that could significantly alter the temperatures on the rise, compared to a cycle in which no new water is introduced. Regarding use of the steam button: unlike other single-boiler machines, in the Sirena, the steam button will not cause the boiler to switch on; it merely activates the thermoblock dedicated for steam.

I have just started using Blue Bottle Coffee's "Roman Espresso" blend, for which they recommend lower temperatures (184F at the portafilter) and longer extraction times; its sensitivity to temperature makes it better for testing than their "Retrofit Espresso". My second shot, 31 sec. at M-1 (falling), was spectacular, one of my best pulls yet. I will try more shots at M-2 & M-3 to see what improvement is possible with these beans. This is where it really comes down to taste.

This is only a beginning, of course; I'm sorry if it looks like trying to chop wood with a sledgehammer. One uses what one has. I am grateful for the knowledge base created over the years by the surfers of other machines. Maybe other Sirena owners will pursue this subject with equal fanaticism and share the results with us.

I hope this helps, even a little bit. After pulling more shots of the Roman Espresso, I'm pretty sure the sweet spot is M-1 for this blend. (Blue Bottle has other blends that demand higher temps, of course.) One still can't draw inferences from pulling shots to say what the gauge increments mean. Until someone hooks up thermocouples to the boiler and portafilter, we really don't know. There's considerable thermometer lag, too -- another reason the gauge is fairly useless for "forward" temp surfing. You'd think, with BMW helping design the Sirena, that they'd give us a "high performance" gauge! Say, something like this...

Good work Roastaroma, on getting use of that uncalibrated thermometer on your machine. Every temp surfer needs a thermometer on the boiler! Nice of them to put that in even if it isn't marked in degrees... you can add those marks yourself.

Try using the 'styrofoam cup/thermometer' test to measure the brew temps at the shower head. If you can correlate brew temps with your boiler temp, you can get consistent accurate brew temps.I find that a difference of 2-3 degrees will put a coffee in or out of it's sweet spot! There is no way you can get consistent temp surfing to this accuracy without using a thermometer. PERIOD!

That thread contained some useful info -- confirming things I had suspected about boiler cycles. (Even shooting in the dark, the muzzle flashes provide a little light!)

You're right -- I guess I'll just have to get one of those digital probe thermometers and do the styrofoam cup thing. I know that won't be as accurate as attaching thermocouples, but it's a step in the right direction.

I've had my two doppios of Roman Espresso, so now I'm ready to present my latest findings. Last night I took temperature readings with a Taylor digital thermometer; I checked its accuracy with a pot of boiling water. Pulling blank single shots at every part of the boiler cycle that Sirena permits, I soon realized why there was no point in putting numbers on the Sirena's temp gauge. Because of the gauge's tremendous lag, each mark on the dial has different values depending on whether the needle is rising or falling! The key point is that "M" (the 12 o'clock mark) is where the water temperature actually peaks; as the needle continues to "rise" to M+3, the temperature is already falling! When the needle finally moves back down, the temperature range may be considered too low for most espresso-brewing.

In other words, what I said earlier about reverse temp surfing applies much sooner than I'd thought. The suitable temp range for espresso, say, 190F to 204F, occurs between M-1 (after the second CLICK) and M+3, only with the needle "ascending". This list will illustrate the pattern, but the specific values are not fixed, not at all! Your temps will certainly vary, but the general arc is consistent. For any given boiler cycle, the peak occurs within M+/-1, right after the boiler element clicks off.

Temp Needle Rising (after the second CLICK)

M-1: 198M: 201M+1: 199M+2: 197M+3: 194

Temp Needle Falling

M+3: 190M+2: 185M+1: 180M: 178M-1: 176M-2: 174M-3: 170

Since the second descending temp range is too low for brewing, at this point one might as well bleed hot water from the steam wand or pull a blank single shot to make the boiler element click on sooner. Depending on your target brewing temp, you may want to have your portafilter loaded in advance, because the little boiler heats up very quickly!

During my testing, I observed another temperature pattern that may affect your brewing: the highest temperatures will be obtained when the Sirena is allowed to warm up for a long time, say 1/2 hour at least. Pulling multiple shots back-to-back (as I did last night), drawing cold water from the reservoir, may lower temperatures overall. In my case, the effect may be more pronounced because of my frigid apartment and its ice-cold tap water. But I think the principle makes sense: with new water pumping through the system constantly, heat tends to dissipate faster, not unlike a cooling system. This may partially account for the dramatically lower temps in the second set of figures.

Because the temp gauge is so unreliable, it makes just as much sense to "time-surf" using a stopwatch to decide when to pull the shot, starting from when the boiler clicks off. Any number of variables could affect the time it takes the needle to reach M+3, and the temps at any point on the dial could vary up to 5F (that is, with the needle moving in the same direction). The gauge's value is not in telling you the temperature, but in telling you generally where you are in the boiler cycle. (Needless to say, we'd all be a lot better off if PIDs were standard equipment throughout the industry!)

OK....I may have found another glitch with trying to use the temperature gauge. It really really may just be a pretty decoration!

I finally got a chance to play around with my machine and was comparing to your notes. My temperature gauge doesn't seem to "hang out" in the same range as yours.

Using your analogy of a clock, if you look at the entire gauge, it runs from about 9:00...past midnight, over to 3:00. Or, in essence, a semi-circle. According to your notes, your machine hangs out around midnight and varies by +/- 3 in each direction.

My machine is quite different. When I turn it on, it slowly raises from the 9:00, past 12:00, and settles at 3:00. Then, as the machine warms/cools, it varies between 12:00 and 3:00.

In fact, 12:00 seems to be the point that it decides it's warm enough to make espresso, and, as I mentioned, 3:00 is the max.

Am I making sense?

If two machines are so wildly different, I think it's time to throw away any idea of using the thermometer. Perhaps, it would be much more appropriate to temp surf like the silvia: raise the boiler to its highest temp, then brew water until you stop hearing steam flashes (or something similar).

I suppose with this much variation between machines, the marks on the dial do not matter as much as the overall pattern of movement, which should not vary. That is, the usable temp range occurs very soon after the boiler clicks off; with the needle "ascending", the temps are actually descending after the first 5 seconds or so. Because Sirena's boiler is smaller than Sylvia's & dissipates heat faster, our surfing technique has to be quicker than in Mark's video -- closer to the Gaggia in style, I reckon. I doubt we'll ever see the sort of steam-flash from the Sirena's group head that Mark demonstrated on the Sylvia; if anything, we need the Sirena's boiler to retain heat, not lose it any faster than it already does.

Mark's method of provoking the boiler into coming on is very similar to what I do, except I use the steam wand to bleed off hot water just until I see the gauge needle fall. If you do it until the lights blink, you've probably drawn too much cold water into the boiler. Even if the lights stay solid, after the first click, one has barely enough time to grind, dose, & tamp before the boiler clicks off. Cowabunga!

In true CoffeeGeek fashion, I just had to go back and do more reverse temp-surfing tonight, this time using a stopwatch along with my thermometer. The level of precision one can achieve this way is a huge improvement over trying to use the bogus temp gauge in the dashboard.

I believe this time the Sirena was able to not just retain heat between shots, but even accumulate heat. No doubt it helped that my apartment was warmer tonight, not the usual "Ice Station Zebra". But I also think a slight variation in my routine contributed to Sirena getting hot and staying hot: instead of pulling shots back-to-back every chance I got, this time, after pulling a shot, I would let the next cycle begin -- and instead of pulling the next shot right away, I would bleed about 1/2 cup of hot water from the steam wand, enough to provoke the boiler to start up again. Then I would pull a shot on the following cycle at my chosen time. I could feel the difference when touching the Sirena's casing; apart from the boiler, there's a lot of steel acting as a heat sink. So I think these new "time-surfing" figures could only be reproduced on a Sirena that has noticeable warmth from the upper deck, esp. behind the temp gauge (the boiler is probably just above the group head).

Using my cellphone's stopwatch, I started timing from the second CLICK that means the boiler element has switched off. Below are listed shot times in x seconds (or minutes/seconds) after "C" (for Click) with temperature readings. A few anomalous temps here illustrate, I believe, the effect of heat accumulating with the accelerated cycles, i.e., some shots pulled later show significantly higher temps than shots pulled earlier. You will also notice long stretches where the temperature hardly changes at all. Quite a difference from the other night!

As you can see, temp-surfing by the clock can still be unpredictable, but the figures suggest "windows of opportunity" where one has better odds of hitting a desired temperature within a given time-frame. Because we can expect variations between individual machines, I would recommend that each owner do his/her own temperature testing and not rely on my chart. Your readings may be a few degrees higher overall, if only because I used a paper coffee cup instead of styrofoam (those are virtually extinct in this city). It seems that on the quest for better espresso, we must consider the thermometer & stopwatch as indispensable as the tamper!

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